optical activity

A sample of material able to rotate the plane of polarization of a beam of transmitted plane-polarized light is said to possess optical activity
(or to be optically active). This optical rotation is the classical distinguishing characteristic (sufficient but not necessary) of
systems containing unequal amounts of corresponding enantiomers. An enantiomer causing rotation in a clockwise direction (when viewed in the direction facing the
oncoming light beam) under specified conditions is called dextrorotatory and its chemical
name or formula is designated by the prefix (+)-; one causing rotation in the opposite
sense is laevorotatory and designated by the prefix (−)-. Materials with optical activity
also exhibit other chiroptic phenomena.